本文選題：金屬鋰電極 + 二次電池��； 參考：《浙江大學》2017年博士論文

【摘要】：隨著電動汽車和消費性電子工業(yè)的發(fā)展,對于高能量密度存儲電源的需求越來越強烈。金屬鋰負極因其擁有高的理論比容量(3860mAhg-1)和較低的電勢(-3.04 V)而成為高能量密度電池系統(tǒng)的理想候選。但是,金屬鋰作為電池負極依然存在兩個非常嚴重的問題:(1)金屬鋰過于活潑,會與電解質(zhì)發(fā)生副反應,電極消耗嚴重,庫倫效率很低;(2)表面SEI容易破損,且表面電位不均勻,導致反應過程中有“枝晶”和“死鋰”的產(chǎn)生,甚至會刺破隔膜,造成安全隱患。庫倫效率低以及安全性能差極大地阻礙了金屬鋰負極的實際應用。目前關于金屬鋰負極改性方法主要有:電解液改性、隔膜改性、集流體改性以及金屬鋰負極直接改性。其中,對金屬鋰負極直接進行改性是研究的重點,也是最有望能夠?qū)崿F(xiàn)商業(yè)化應用的方法之一。本論文主要采用以下方法對金屬鋰負極進行了改性研究:(1)利用原位反應方法在金屬鋰表面制備Li_3N薄膜,得到Li_3N/Li復合負極材料。在該反應中的主要反應參數(shù)有:反應時間、反應溫度以及通氣流量。利用控制變量法研究不同反應參數(shù)對Li_3N/Li復合負極電化學性能的影響。在最優(yōu)反應參數(shù)下制備Li_3N/Li復合負極材料,將其與純Li負極材料進行比較,表現(xiàn)出了較好的電化學性能,且循環(huán)后的枝晶形貌被明顯抑制,副反應產(chǎn)物也較少。說明表面包覆Li_3N不僅可以保護金屬鋰不與電解液接觸,減少副反應的發(fā)生,還可以抑制枝晶的形成,提高安全性能。(2)采用磁控濺射的方法在金屬鋰表面沉積了a-C納米薄膜�？刂拼趴貫R射得到a-C包覆層厚度不同的a-C/Li負極。對其進行電化學性能測試,發(fā)現(xiàn)隨著沉積時間的延長,a-C/Li負極的阻抗性能下降,鋰離子傳輸受到阻礙。對循環(huán)后的電極表面進行SEM觀察,發(fā)現(xiàn)沉積時間越久,對枝晶生長的抑制作用越明顯。因此,沉積時間過長或過短在本實驗中都會減弱a-C膜對金屬鋰負極電化學性能的促進作用。(3)結合Li_3N薄膜的高離子電導率和磁控濺射a-C納米薄膜的均勻致密性,采用磁控濺射方法在金屬鋰負極表面沉積摻氮非晶碳(a-CN_x)膜。研究了不同含氮量對a-CN_x薄膜性能的影響,控制氮氣分壓分別為0 sccm,5 sccm和10 sccm,發(fā)現(xiàn)氮氣分壓為10 sccm時a-CN_x/Li負極的電化學性能最好。通過共聚焦原位測試,分別觀察了純Li負極、a-C/Li負極以及a-CN_x/Li負極(10sccm)在不同電流密度下的枝晶生長情況。其中,純鋰負極在1 C電流密度下即產(chǎn)生明顯枝晶,刺破隔膜;a-C/Li負極在5 C電流密度下才觀察到有刺猬狀的枝晶產(chǎn)生;而a-CN_x/Li負極(10 sccm)所對應的隔膜在10 C電流密度下才被穿透。這一方面說明,表面包覆非晶碳薄膜或者摻氮非晶碳薄膜都可以抑制枝晶的形成;另一方面說明,相對于不摻雜N元素的非晶碳薄膜而言,摻雜了N元素的碳氮復合薄膜對枝晶的生長具有更好的抑制作用。(4)采用抽濾法制備微米級的GO紙膜,在水合肼中還原成為rGO薄膜,利用機械壓實法得到rGO/Li復合負極材料。通過循環(huán)后的平面和斷面形貌觀察,純Li負極的表面有明顯的枝晶形貌且斷面形貌發(fā)生坍塌;而rGO/Li復合負極的平面和斷面形貌都保持良好。通過金屬鋰對稱電池以及Li-Cu半電池體系進行電化學性能測試,可以看出rGO包覆對提高金屬鋰負極的循環(huán)穩(wěn)定性有明顯的促進作用。最后對不同次數(shù)下rGO/Li負極的SEM形貌圖進行觀察,描述了鋰枝晶的生長過程。(5)采用自動鋪展法在金屬鋰片表面包覆了納米級GO薄膜。選用合適的有機溶劑來分散石墨烯粉末非常重要,我們對乙醇、乙腈、乙醚以及DMC四種有機溶劑進行研究,其中DMC既可以溶解極性的GO粉末,與金屬鋰之間也有足夠的穩(wěn)定性。對純Li負極以及GO/Li負極在金屬鋰對稱電池以及鋰硫全電池體系中的電化學性能進行比較,發(fā)現(xiàn)GO膜包覆一方面可以保護金屬鋰負極不與電解液接觸,提高其電化學性能;另一方面可以抑制枝晶的形成,提高循環(huán)穩(wěn)定性。(6)采用熔融法制備了垂直石墨烯(VG)與金屬鋰的復合負極材料。首先利用磁控濺射技術在VG陣列表面沉積一層Si,使“疏鋰性”的VG陣列轉變成“親鋰性”的Si@VG復合陣列。然后在200℃下將液態(tài)鋰灌入陣列結構之中,得到Si@VG/Li復合負極材料。VG陣列的多孔結構可以控制金屬鋰的體積膨脹,并抑制枝晶的形成,使其具有良好的電化學穩(wěn)定性。除此之外,Si@VG/Li復合負極材料在Li-S全電池體系中也表現(xiàn)出了良好的循環(huán)穩(wěn)定性。
[Abstract]:With the development of electric vehicles and consumer electronics industry, the demand for high energy density storage power is becoming more and more intense. Metal lithium anode is the ideal candidate for high energy density battery system because of its high theoretical specific capacity (3860mAhg-1) and lower potential (-3.04 V). However, the lithium metal is still two as the negative electrode of the battery. A very serious problem: (1) the metal lithium is too active, will have a side reaction with the electrolyte, the electrode consumption is serious, the efficiency of the Kulun is very low; (2) the surface SEI is easily damaged and the surface potential is not uniform, which leads to the production of "dendrite" and "dead lithium" in the reaction process, and even the septum will be pierced to cause the hidden danger. The efficiency and safety of Kulun is low and safe. The performance difference greatly hinders the practical application of metal lithium anode. At present, the main methods for the modification of lithium negative electrode include electrolyte modification, membrane modification, fluid collector modification and direct modification of metal lithium anode. This paper mainly uses the following methods to study the modification of metal lithium anode: (1) the preparation of Li_3N film on the surface of lithium metal by the in-situ reaction method, and the Li_3N/Li composite anode material is obtained. The main reaction parameters in this reaction are reaction time, reaction temperature and ventilation flow. The different reactions are studied by the control variable method. The effects of parameters on the electrochemical performance of Li_3N/Li composite negative electrode. Li_3N/Li composite negative electrode was prepared under the optimal reaction parameters. Compared with the pure Li negative electrode, it showed good electrochemical performance, and the dendrite morphology was obviously suppressed and the side reaction products were less. The surface coating Li_3N not only can protect gold. Lithium does not contact with the electrolyte, reduces the occurrence of the side reaction, inhibits the formation of the dendrite and improves the safety performance. (2) the a-C Nanothin film is deposited on the surface of the lithium metal by magnetron sputtering. The magnetron sputtering is used to control the a-C/Li negative electrode of the a-C coating with different thickness. The resistance performance of the a-C/Li negative electrode decreased and the lithium ion transmission was hindered. SEM observation on the surface of the electrode after the cycle found that the longer the deposition time was, the more obvious the inhibition effect on the dendrite growth. Therefore, the longer or too short deposition time will weaken the effect of the a-C film on the electrochemical performance of the lithium anode. (3) Combined with the high ionic conductivity of Li_3N films and the uniform densification of a-C Nanothin films by magnetron sputtering, the nitrogen doped amorphous carbon (a-CN_x) films were deposited on the surface of metal lithium anode by magnetron sputtering. The effects of different nitrogen content on the properties of a-CN_x films were studied. The nitrogen partial pressure was 0 SCCM, 5 SCCM and 10 SCCM respectively, and the nitrogen partial pressure was found to be 10 s. The electrochemical performance of a-CN_x/Li negative electrode was the best at CCM. The dendrite growth of pure Li negative electrode, a-C/Li negative electrode and a-CN_x/Li negative electrode (10sccm) was observed at different current densities by confocal in-situ test. The pure lithium negative electrode produced obvious dendrites and pierced the diaphragm at 1 C current density, and a-C/Li negative electrode was at 5 C current density. The hedgehog like dendrites were observed, and the a-CN_x/Li negative (10 SCCM) diaphragm was penetrated at 10 C current density. In this respect, the surface coating of amorphous carbon film or nitrogen doped amorphous carbon film can inhibit the formation of dendrites; on the other hand, the phase is doped for amorphous carbon films without N elements. The carbon and nitrogen composite film of N element has a better inhibitory effect on the growth of dendrite. (4) the micrometer GO paper film was prepared by the extraction method and reduced to rGO film in hydrazine hydrate. The rGO/Li composite negative material was obtained by mechanical compaction. The surface of pure Li negative electrode surface has obvious dendrite morphology through the plane and cross section morphology after the cycle. The plane and surface morphology of the rGO/Li composite negative electrode remained well. The electrochemical performance test of the lithium symmetric battery and the Li-Cu semi battery system showed that the rGO coating could improve the cyclic stability of the lithium anode. Finally, the SE of the rGO/Li negative electrode at different times was SE. M morphologies are observed and the growth process of lithium dendrites is described. (5) the nano scale GO film is coated on the surface of lithium metal sheet by automatic spreading method. It is very important to choose the suitable organic solvent for dispersing the powder of graphene. We have studied the four organic solvents of ethanol, acetonitrile, ether and DMC, in which DMC can dissolve the GO of polarity. There is sufficient stability between the powder and the lithium metal. The electrochemical performance of pure Li negative electrode and GO/Li negative electrode in the lithium and sulfur full battery system is compared. It is found that the coating of the GO film can protect the lithium negative electrode from the electrolyte contact and improve its electrochemical performance; on the other hand, the dendrite can be suppressed. It is formed to improve the cyclic stability. (6) a composite anode material for vertical graphene (VG) and lithium metal is prepared by melting method. First, a layer of Si is deposited on the surface of VG array by magnetron sputtering, and the "lithium sparsely" VG array is transformed into a "lithium-dependent" Si@VG composite array. Then the liquid lithium is poured into the array structure at 200. The porous structure of the Si@VG/Li composite anode material.VG array can control the volume expansion of the lithium metal and inhibit the formation of the dendrite, so that it has good electrochemical stability. In addition, the Si@VG/Li composite negative electrode also shows good cyclic stability in the Li-S full battery system.

【學位授予單位】：浙江大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TM912

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相關博士學位論文 前3條

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本文編號：1822580